Acne vulgaris is the most common skin disease in the United States. It is estimated that 40 to 50 million Americans have acne, including 80% of people between the ages of 11 and 30. The annual direct costs associated with the treatment of acne exceeded $2.8 billion in 2007, with the majority of those costs attributable to prescription drugs. In addition, acne causes both physical and psychological effects, including permanent scarring, anxiety, depression, and poor self-esteem. Even in cases of mild acne, the social stigma associated with the disease frequently results in significant emotional distress and other psychological issues. Due to its social impact, frequency of recurrence of relapse, and necessary maintenance over a prolonged course of therapy, the American Academy of Dermatologists have recommend that acne vulgaris be re-classified and investigated as a chronic disease.
Acne vulgaris results from the complex interplay of four major pathogenic factors: 1) overproduction of sebum by the sebaceous gland; 2) abnormal keratinization in the follicle; 3) colonization of the hair follicles by the anaerobic, lipophilic bacterium Propionibacterium acnes, or P. acnes; and 4) release of inflammatory mediators into the skin. All acne lesions begin when the combination of excess sebum and abnormal epithelial desquamation clog up a follicle, forming a microscopic lesion known as a microcomedo. The anaerobic, lipid-rich environment of the microcomedo provides an ideal location for P. acnes proliferation. Each microcomedo may progress to form a non-inflammatory open or closed comedone (commonly referred to as a “blackhead” or “whitehead,” respectively), or an inflammatory lesion that may be further categorized as a papule, pustule, nodule, or cyst.
The complexity of the disease may require multiple treatments that may span oral and topical antimicrobials, oral and topical retinoids, oral contraceptives and other prescription skin cleansers. The most effective therapies for acne are those that may safely address more than one of the major causes of acne pathogenesis.
Antibiotics were the first successful acne treatment due to their antimicrobial and anti-inflammatory properties. Both topical and systemic antibiotics have been very successful, but the protracted treatment periods required have led to the development of resistance of P. acnes and in other non-targeted (and potentially pathogenic) commensal organisms. Combining antibiotics with topical retinoids targets three of the four major pathogenic factors associated with acne (all but sebum production). The oral retinoid isotretinoin (e.g., Accutane®) is the only drug-implicated to affect all four pathogenic factors associated with acne. However, the severity of its potential side effects (known teratogen and linked to depression, psychosis and suicide) has limited its use and led to numerous lawsuits.
While the problems associated with isotretinoin are the most severe, all of the current acne medications have some adverse effects. The majority of topical treatments lead to dryness, irritation and peeling of the skin, and oral antibiotics may cause gastrointestinal tract irritation, photosensitivity of skin, headache, dizziness, anemia, bone and joint pain, nausea and/or depression.
The most commonly prescribed drugs from acne are antibiotics, including benzoyl peroxide, clindamycin and erythromycin, either alone or in combination, and retinoids, including adapalene, tretinoin and tazarotene, either alone or in combination with an antibiotic. Treatments may include combination drugs or combination therapies. For example, a retinoid may be prescribed for application in the morning and an antibiotic for application in the evening. Each of these commonly prescribed drugs, however, has disadvantages that often reduce the effectiveness of the therapy.
For example, benzoyl peroxide may be the most effective topical medicine for acne and may result in a rapid reduction in P. acnes. It also does not induce drug resistance in the P. acnes and, when combined with other antibiotics, may reduce the rate at which drug resistance develops. However, benzoyl peroxide commonly results in irritation and dryness of the skin and bleaches fabric. Additionally, about 2% of patients have an allergic reaction to benzoyl peroxide.
Clindamycin and erythromycin as monotherapies may be limited in effectiveness because of the development of drug resistant strains of P. acnes. In fact, it is estimated that up to 75% of P. acnes is already resistant to these antibiotics. However, these products are available in a number of different bases and are typically non-irritating and non-staining.
Retinoids mainly target comedonal acne but may also reduce inflammatory lesions. Retinoids, however, are slow to produce visible results and may produce irritation, redness and peeling. In light of these limitations of retinoids, they are typically not used alone.
Combinations of these various drugs are also available. For example, clindamycin and benzoyl peroxide combination drugs are available as well as combinations of erythromycin and benzoyl peroxide, combinations of adapalene and benzoyl peroxide and combinations of clindamycin and tretinoin. These drugs may have improved efficacy over the individual drugs but also carry with them the limitations of their constituents. Furthermore, none of these combinations address all four of the causes of acne.
In addition to the limitations of the available drugs themselves, a number of additional factors may affect compliance with a treatment regime and, therefore, may reduce the regime's overall efficacy. These factors include the degree of irritation of the product, the time to noticeable results, the aesthetics of the product, the repeatability required, the effect on clothing and other items the product comes in contact with and the convenience of the packaging and storage of the product. If the product irritates the skin, the patient may discontinue use. If the product takes too long to provide visible results, the patient may get frustrated and stop treatment. If the product feels greasy, leaves a visible residue or is powdery and grating, the patient may be less likely to maintain the regime. If the product stains or bleaches clothes, bedding or other fabrics, the patient may discontinue its use. Finally, if the product is too difficult to use or store, the patient may be unlikely to use it or to follow the use and/or storage directions.
It may be difficult to obtain compositions that address some or all of these factors. It may be even more difficult to obtain anhydrous compositions that address some or all of these factors. As such, new compositions and methods for making such compositions may be desirable.